Recently, there have been widely used push-switches for vehicles, of a push-operated type, for controlling stop lamps following depressing operation of the brake pedal, or more specifically, for turning on the stop lamps when the brake pedal is depressed and turning off the lamps when the depression is released. A conventional-art example of such push-switches for vehicle (hereinafter called “PSV”) will be described with reference to FIG. 3 and FIG. 4. FIG. 3 is a sectional view of PSV of conventional art. In FIG. 3, case 1 formed of an insulating resin material substantially in a box shape with an opening provided in its top plate has a plurality of fixed contacts 3 embedded in the top plate with their terminal portions 3A projecting from the underside of the top plate.
Further, there is provided conductive, metallic movable contact 4 upwardly urged by contact pressure spring 5 to elastically contact with fixed contacts 3. Thus, a plurality of fixed contacts 3 are electrically connected by movable contact 4 thereby establishing a switch contact. Further, contact pressure spring 5 in its slightly compressed state is mounted between movable contact 4 and the inner bottom of case 1.
The opening provided in the top plate of case 1 is covered by cover 7. Return spring 6 in a coil shape in its slightly compressed state is inserted between the underside of operating member 2 and the inner bottom of case 1 so that operating portion 2 is urged upward.
Cover 7 is provided with hollow cylindrical portion 7A projecting upward. Within cylindrical portion 7A, there is inserted operating shaft 2A of operating member 2 for vertical movement, while the upper end of operating shaft 2A is upwardly protruded from hollow cylindrical portion 7A. PSV is thus constructed.
PSV constructed as described above is generally mounted forwardly of the brake pedal (not shown) of a vehicle with operating shaft 2A of operating member 2 pressed in by an arm or the like. Further, terminal portions 3A of fixed contacts 3 are connected with stop lamps via connectors or the like. More specifically, in a state where the brake pedal is not depressed, operating shaft 2A of operating member 2 is pressed downward to compress contact pressure spring 5 and return spring 6 so that movable contact 4 is moved downward to be separated from fixed contacts 3. As a result, a state where a plurality of fixed contacts 3 are electrically disconnected is brought about and hence the stop lamps are turned off.
When the brake pedal is then depressed, the arm is separated from operating shaft 2A so that the pressing force acting thereon is released. As a result, operating member 2 is moved upward by the elastic restoring force of return spring 6 and, at the same time, movable contact 4 is brought into elastic contact with fixed contacts 3 by being pressed by contact pressure spring 5. Thus, the plurality of fixed contacts 3 are brought into their electrically connected state so that the stop lamps are turned on.
Electric bulbs, LEDs, or the like are generally used as the stop lamps turning on and off in the above described manner. When electric bulbs are used, a relatively large current, e.g., around 10 A at DC 12V, is supplied. When, on the other hand, LEDs or the like are used, a relatively small value of current, e.g., 0.5A-1A at DC 12V, is supplied. Incidentally, an example of PSV having the configuration as described above is disclosed in Japanese Patent Unexamined Publication No. 2003-151398.
In above described conventional PSV, however, movable contact 4 and fixed contact 3 as shown in their sectional view of FIG. 4 are in contact with each other at one point on their surfaces. Therefore, in case of such PSV is used for stop lamps employing LEDs or the like operating with a small value of current and oxide film is formed on the surfaces of fixed contacts 3 and movable contact 4, there arises a possibility of an unstable contact occurring between the contacts.
The present invention has been made to solve such a problem encountered in conventional art and is aimed at realization of PSV providing stabilized contacts.